This invention relates to the testing of the degree of vacuum in a evacuated vial, and in particular to a method and apparatus for testing the degree of vacuum by ionizing the gas within the vial and measuring the ionization current.
Evacuated vials can be tested without opening the vial or inserting any test probe or other device into the vial. For example, U.S. Pat. No. 1,917,465 to Schweitzer discloses a process and apparatus for testing a vial in which a high voltage is applied across an evacuated vial in order to cause the gas within the vial to glow. A similar process and apparatus is found in U.S. Pat. No. 2,519,807 to Yeater. Still other variations of this basic process and apparatus are found in U.S. Pat. No. 2,633,486 to Sweet, U.S. Pat. No. 3,839,655 to Heigland and U.S. Pat. No. 3,979,668 to Samulowitz. In the prior art set forth above, a high voltage is usually applied to the vial in order to cause the gas within the vial to ionize. When the gas ionizes, the color of the gas will then determine the degree of vacuum. Usually, a photocell is used to determine the amount of vacuum.
One of the problems of the prior art is that the high voltage applied to the vial must be sustained in order to cause ionization, and in certain instances, the high voltage can change the characteristics of the substance within the vial. This is unsatisfactory for many uses, particularly in the medical field, and therefore, for gases which do not ionize well, it is impossible to test the vacuum within a vial using prior art methods without altering the characteristics of the contents of the vial.
U.S. Pat. No. 2,524,929 to Razek and U.S. Pat. No. 2,734,628 to Schlayer disclose a method of testing the vacuum within an evacuated vial by shining a light through the vial and then detecting the light with a photocell. Like the prior art patents discussed above, however, both of these patents require a high voltage to be applied to the vial to cause ionization. The light which is shined through the vials is used simply for detecting the degree of vacuum by determining the ionization within the vial. Thus, these patents sufer the same deficiency of having the possibility that the contents of the vial can be altered by lengthy sustained application of high voltage to the vial in order to cause ionization.